The Universal Mobile Telecommunication Service (UMTS) standard provides a compatibility standard for cellular mobile telecommunications systems. The UMTS standard ensures that user equipment (UEs) operating in a UMTS system can obtain communication services when operating in a system manufactured according to the standard. To ensure compatibility, radio system parameters and data transfer procedures are specified by the standard, including protocols governing digital control messages and bearer traffic that are exchanged over an air interface.
The UMTS standards provide, in 3GPP TS 25.344 (Third Generation Partnership Project Technical Specification 25.344) v0.5.0, 3GPP TS 23.246 v1.1.0, 3GPP TS 23.846 v6.1.0, 3GPP TS 25.331 v5.6.0, and 3GPP TS 25.346 v6.3.0, for a provision of a Multimedia Broadcast/Multicast Service (an MBMS service) by a UMTS communication system to UEs serviced by the system and subscribed to the service. The MBMS service provides for a multicast of MBMS data, typically in a format of Internet Protocol (IP) data packets, to the subscribed UEs. In order to ensure that the air interface resources of the UMTS communication system are not wasted, the system first estimates the number of recipients, that is subscribed UEs, in a cell providing MBMS data. Based on the estimated number of recipients, a Radio Network Controller (RNC) included in a UMTS infrastructure determines whether to establish a Point-To-Multipoint (PTM) communication channel in the cell or a Point-To-Point (PTP) communication channel to each recipient.
When the RNC determines to establish a PTM communication channel in each of multiple cells, that is, at each of multiple corresponding Node Bs, the RNC may then multicast the MBMS data via a Forward Access Channel (FACH) of each cell, which FACH is mapped to a Secondary Common Control Physical Channel (S-CCPCH) of the cell. A UE receiving a same MBMS data stream via the S-CCPCH of each of the multiple Node Bs may then combine the data streams. By combining a data stream received from each of multiple Node Bs, significant system gain may be obtained. However, in order to obtain the benefits of soft combining, the UE must be able to synchronize the MBMS data received by the UE via each Node B of the multiple Node Bs.
Therefore, a need exists for a method and apparatus that permits a UE to synchronize MBMS data received by the UE via each Node B of multiple Node Bs.